Permutations and Combinations in Python

permutations_combinations.py

def permute(l) :
    if len(l) == 1 :
        yield l
    else :
        for i in range(len(l)) :
            for j in permute(l[:i] + l[i + 1:]) :
                yield [l[i]] + j

def combinations(l, r) :
    if r == 1 :
        for i in l :
            yield [i]
    elif len(l) == r :
        yield l
    else :
        for j in combinations(l[1:], r - 1 ) :
            yield j + [l[0]]
        for j in combinations(l[1:], r) :
            yield j


# Non-yield version
def perm(s, pre = '') :
    if len(s) :
        for i in range(len(s)) :
            perm(s[:i] + s[i + 1:], pre + s[i])
    else :
        print pre